Many medical patients suffering from any one of a variety of lung ailments are often prescribed supplemental oxygen therapy so that the patient could breath oxygen-enriched air throughout the day and sometimes throughout the night. Earlier supplemental oxygen therapy employed a nasal cannula system operably connected between a tank of compressed oxygen and the patient's nose. Oxygen was continuously delivered to the patient throughout the patient's entire breathing cycle. This method of continuously delivering oxygen to the patient throughout the patient's breathing cycle was considered wasteful because much of the oxygen dissipated into the ambient air environment. Better methods of delivering oxygen to the patient were later developed which included improved equipment that would only deliver oxygen to the patient during the inhalation phase of the patient's breathing cycle. Usually, this improved equipment employed a demand valve which opened to deliver supplemental oxygen to the patient only when the patient inhaled. Numerous types of demand valves are well known in the prior art.
One such demand valve is described in U.S. Pat. No. 5,360,000 to Carter. This demand valve is compact, simplified and totally pneumatic. The demand valve which is coupled between a source of pressurized gas such as oxygen and the patient includes a valve body having a gas flow passageway and pneumatically-coupled sensing and slave diaphragms. The slave diaphragm is interposed in the gas flow passageway and prevents gas from flowing during the exhalation phase of the patient's respiratory cycle. During inhalation, which is sensed by a sensing diaphragm, the slave diaphragm moves to open the gas flow passageway, thus permitting flow of gas to the patient.
U.S. Pat. No. 5,666,945 to Davenport, the disclosure of which is incorporated herein by reference, describes a pneumatically-operated gas demand apparatus which overcomes many of the deficiencies of prior devices. The Davenport apparatus includes cooperating supply and sensing valves in interruptible fluid communication between a recipient (or patient) and at least a first source of pressurized gas. The supply valve includes a supply valve housing with a first diaphragm member disposed therein. Similarly, the sensing valve includes a sensing valve housing and a second diaphragm member disposed therein. The Davenport apparatus is constructed such that, when recipient inhales, the second diaphragm member assumes a flow-causing position and the first diaphragm member assumes a flow-supplying position whereby pressurized respiratory gas is delivered to the recipient. When the recipient exhales, the second diaphragm member assumes a flow-stopping position and the first diaphragm member assumes a flow-blocking position, thereby preventing delivery of the respiratory gas to the recipient.
The Davenport apparatus performs its intended functions quite effectively. However, its supply (or pilot) valve is somewhat complicated in design, labor-intensive in construction and susceptible to gas leaks. The supply valve housing comprises first and second housing parts including cooperating passageways for providing fluid communication between the supply valve and the sensing valve. As presently constructed, both the first and second housing parts must be drilled or bored to create portions of a first of the passageways. An O-ring or similar sealing means must be provided at the juncture of the first passageway portions in order to prevent respiratory gas leakage from between the first and second housing parts. At least one of the first and second housing parts must also be counterbored to accommodate the O-ring. The second housing part is radially drilled or bored to produce a second passageway which intersects the first passageway. After formation, the second passageway must be plugged or otherwise sealed from the ambient atmosphere. So constructed, the plug represents another site from, through or around which respiratory gas may leak from the valve housing. The many construction steps of the Davenport supply valve, coupled with its potential for gas leakage at more than one site, render the valve somewhat onerous to assemble and less than optimal from a performance perspective.
An advantage exists, therefore, for a supply valve for a pneumatically-operated gas demand apparatus which is simple in design, easily fabricated and assembled and resistant to gas leakage.